Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WaaSMedicSvc - Windows Update Medic Service.
You'll see "Start" Reg_DWORD key. Open this and Value Data should be set to 1 or 2. Changing this option to 4 disables the service.
go to Services and check Windows Update Medic Service (WUMS should be disabled now.) Windows Update (WU), Delivery Optimization (DO), and Update Orchestrator (UO) can now be disabled via Services, and with WUMS disabled, this should stop WU, DO, and UO services from being reactivated.